As for the other two items, I would suggest grenade and RPG. They both have considerable area of effect, and hence they are very effective when dealing with a cluster of enemies. RPG is easier to handle and it can be fired almost instantly without having to take aim – but it comes at a higher price. Focus fire is great when you are up against a very tanky Boss. Bosses or tanky enemies will appear in some of the stages in the Challenge mode. If you can’t take them down fast enough, they can pose a real threat.